1. Field of the Invention
The present invention relates generally to manufacturing processes involving the coating of substrates. More particularly, the present invention relates to apparatuses and methods for identifying a particular side of a substrate that is sputtered on both sides.
2. Description of the Related Art
Various manufacturing processes involve coating multiple layers of materials on substrates. Materials are coated onto substrates using various methods including but not limited to evaporation, chemical vapor deposition (CVD), plasma vapor deposition (PVD), and sputtering. A basic sputtering operation includes bombarding a target material with ions to release atoms from the surface of the target. The released atoms are directed towards the substrate so that they become deposited on the surface of the substrate. To build up the desired multiple layers of different materials, the sputtering operation is repeated with a previously coated substrate, using targets of different materials in each sputtering operation.
In some applications it is necessary or desirable to sputter identical layers onto both sides of the substrate. One application where it is necessary to deposit layers onto both sides of a substrate is magnetic media used in conventional hard disk drives for memory storage.
Conventional disk drives are used to magnetically record, store and retrieve digital data. Data is recorded to and retrieved from one or more disks that are rotated at more than one thousand revolutions per minute (rpm) by a motor. The data is recorded and retrieved from the disks by an array of vertically aligned read/write head assemblies, which are controllably moved from data track to data track by an actuator assembly.
The three major components making up a conventional hard disk drive are magnetic media, read/write head assemblies and motors. Magnetic media, which is used as a medium to magnetically store digital data, typically includes a layered structure, of which at least one of the layers is made of a magnetic material, such as CoCrPtB, having high coercivity and high remnant moment. The read/write head assemblies typically include a read sensor and a writing coil carried on an air bearing slider attached to an actuator. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning disks to fly the head assembly in a closely spaced relationship to the disk surface. The actuator is used to move the heads from track to track and is of the type usually referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disk drive housing closely adjacent to the outer diameter of the disks. Motors, which are used to spin the magnetic media at rates of higher than 10,000 revolutions per minute (rpm), typically include brushless direct current (DC) motors. The structure of disk drives is well known.
Magnetic media is typically made by depositing multiple layers onto both sides of a substrate. By depositing a multi-layer magnetic media structure onto both sides of the substrate, twice as much information can be recorded onto each disk because both sides of the disks are used. Typically, two read/write heads are used when both sides of the magnetic media are utilized. Each side of the disk has its own read/write head to record and retrieve information from their respective sides.
FIG. 1A illustrates a conventional magnetic media structure comprising a substrate 110, a first nickel-phosphorous (NiP) layer 115, a second nickel-phosphorous (NiP) layer 116, a first seed layer 120, a second seed layer 121, a first magnetic layer 125, a second magnetic layer 126, a first protective layer 130 and a second protective layer 131. The substrate 110 is typically made of aluminum or high quality glass having few defects. The first nickel-phosphorous (NiP) layer 115 and second nickel-phosphorous (NiP) layer 116 are amorphous layers that are usually electrolessly plated or sputtered onto both sides of substrate 110. The NiP layers are used to enhance both the mechanical performance and magnetic properties of the disk. The NiP layers enhance the mechanical properties of the disk by providing a hard surface on which to texture. The magnetic properties are enhanced by providing a textured surface that improves the magnetic properties including the orientation ratio (OR).
First seed layer 120 and second seed layer 121 are typically thin films made of chromium that are deposited onto the NiP layers 115 and 116 respectively forming the foundation for structures that are deposited on top of them. First magnetic layer 125 and second magnetic layer 126, which are deposited on top of first seed layer 120 and second seed layer 121 respectively, typically include a stack of several magnetic and non-magnetic layers. The magnetic layers are typically made out of magnetic alloys containing cobalt (Co), platinum (Pt) and chromium (Cr), whereas the non-magnetic layers are typically made out of metallic non-magnetic materials. Finally, first protective overcoat 130 and second protective overcoat 131 are thin films typically made of carbon and hydrogen, which are deposited on top of the first magnetic layer 125 and second magnetic layer 126 respectively, using conventional thin film deposition techniques.
The magnetic media structure described with reference to FIG. 1A is usually constructed using conventional thin film deposition techniques such as sputter deposition. When a single disk sputtering process is used, a single substrate is usually processed in a sputtering system by moving the substrate in front of a target and sputter depositing a layer of material onto the substrate. The substrate is usually supported with a holder that has minimal contact on the substrate such as the one illustrated in FIG. 1B. The substrate holder of FIG. 1B supports a substrate with three support rods 160, 165 and 170 that make contact with the disk on the edge of the disk. This support structure is used because the surface of the disk is minimally affected allowing for the entire surface to be used for recording data.
In many applications, including the magnetic disk described with reference to FIG. 1A above, it is advantageous to distinguish between the two sides of the disk. Typically, one side is referred to as the A-side of the disk whereas the other side is referred to as the B-side of the disk. This is especially true in areas of media manufacturing because both sides of the disk are processed. Once a disk is processed it is very difficult to distinguish one side from the other side without maintaining side integrity throughout the process. Maintaining side integrity is not a reliable method of determining the sides of the disks because it is very difficult, if not impossible, to know if side integrity has been maintained throughout the process because typical processing step often involve many steps where the disks are removed from their cassettes and processed before returning the disks back into their cassettes.
There are many reasons why it is important to know which side of the disk is the A-side and which side of the disk is the B-side including failure analysis and quality control. Failure analysis work often requires an engineer to determine-which side of the disk is defective so that the engineer can timely find the problem causing the defect. Quality control also requires one to know which side of the disk has a defect because it insures quick notification to customers of which side of a disk they should use.
Therefore what is needed is a system and method that allows for reliable and quick identification of the disk side at different stages in the manufacturing process.